The cell is the smallest and basic fundamental unit of life. Cells are independent of each other, they take up the nutrients from food, convert those nutrients into energy, helps in excreting wastes, respond to the stimuli and carrying out specialized functions.
They provide structural support to the body and also contains the body's hereditary material and can replicate it.
Reasons why cells are small
Cells are usually small in order to maximize their higher surface area to volume ratio. The higher ratio in turn allows more molecules and ions to diffuse across the cell membrane per unit of cytoplasmic volume. this enables the cell to be able to get the nutrients in and the wastes out at a faster rate
If the cells were large it would mean a smaller surface area to volume ratio. This means only little material would be able to move across the cell membrane and the cell would not be able to accommodate the increased cellular volume. This may lead to the cell ceasing to function.